Toning photographic prints



Patented Feb. 11, 1941 UNITED STATES PATENT OFFICE 2,231,201 some rno'rocmrmc rnmrs Francis E. Snyder and Henry W. Bimbach, New 7 York, N. Y., assignors to Tcchnico, Inc.,-New York, N. Y., a corporation of Delaware No Drawing. Original application January 18, g 1938, Serial N0. 59,794, 110W Patent No. 2,171,609,

dated September 5, 1939.

Divided and this application June 20, 1939, Serial No. 280,216

' '12 Claims. (01. 95- -98) is to provide a procedure for the red-toning of photographic prints which avoids disadvantages 15. of toning processes heretofore employed. A further object of the present invention is to provide improved procedures for red-toning photographic prints by the use of which toned prints of the desired'color, brilliance, and clar-L 20 ityin detail of image can be quickly and inexpensively produced. I

Another object of the present invention is to provide an improved process for toning the redcoior component image for multi-color photog- 25 raphy.

Other objects and advantages of the invention will become apparent during the course of the following description.

In its broad aspect, our process consists in 30 transforming the silver image on a photographic print into a latent or patent metallic salt image, while converting the metallic silver present into a compound readily removable in a suitable solvent, such as hypo, and transforming 35 the metallic salt image into an image of a red color having approximately the same form and gradation as the original print, the silver compound present being removed from the print desired color by treatment with a coiorprecipi-' 50 tant.

In preferred practice, the finished print is to be tonedmagenta, which is the primary red of color photography. To produce the desired result, the print is first preferably treated to 5 transform the silver image into an image of nickel ferrocyanide which is subsequently reacted upon with a suitable color precipitant to deposit a pigment of a magenta colo The general procedure followed in the practice of the present invention involves the initial treatment of a silver photographic print in a bath containing nickel ionsand-also ferricyanic acid ions, the bath containing a suitable reagent to prevent the precipitation of nickel ferricyanide. When the silver print is immersed m in a bath of the character referred to, it appears that the' metallic silver present on the print eiiects the precipitation of nickel ferrocyanide, the silver functioning as a reducing agent. 1 Since the nickel ferrocyanide will be deposited only where silver particles occur on the print and to a degree corresponding to the con centration of the silver particles in any given portion of the print, the nickel ferrocyanide particles will have substantially the same distribution as the original silver particles. In serving as a reducing agent to efiect the precipitation of nickel ferrocyanide, the metallic silver is converted into silver oxide or hydroxide, which, by virtue of the ferricyanic acid ions present, is converted into silver ferricyanide.

The silver ferricyanide may be removed from the print, as in a hypo solution, either during the first stage of treatment of the print or after the second stage of the toning operation. In either case, the print which has nickel ferrocyanide deposited thereon is treated with a color precipitant to convert the nickel ferrocyanide into a pigment of a red color.

The treating bath employed in the first stage of the process comprises an aqueous medium to which has been 'added a soluble ferricyanide of a metal which will not form an insoluble compound with any other ion present in the treating bath; a soluble salt of nickel; a reagent ca- 40 pable of preventing the precipitation in the bath of a ferricyanide of nickel; anacid; and, preferably, an aqueous solution of formaldehyde, such as commercial formalin. Where, as in some modifications of the process, the silver content of the print is to be removed therefrom in the first-stage treatment, the treating bath should include a solvent for the silver compound 'all of the constituent reagents at one time, it is advisable to withhold the addition of the solu- 55 ble ferrlcyanide until Just prior to the use of the treating bath. I

In preparing the first-stage treating bath, we

may employ any soluble ferricyanide of a metal which does not form an insoluble compound with any other ion present in the treating bath, such as potassium, sodium or ammonia ferricyanide. Our preferenceis for potassium ferricyanide.

Any soluble salt of nickel may be employed in the preparation of the treating bath, such as the nitrate, sulfate, acetate, chloride, bromide, iodide or the like. Where reference is made to a "soluble salt it is meant that the salt will provide a solution of more than one per cent. concentration at 20 C. I

For the purpose of acidifying the treating bath we prefer to employ citric acid although other acids will serve, including both organic and in-' organic acids, such as tartaric, acetic, oxalic, hydrochloric, nitric, or the like.

It is necessary to employ in the treating bath a reagent which will prevent the precipitation of a ferricyanide of nickel, while permitting the precipitation of the ferrocyanide of nickel. For this purpose we employ any freely soluble salt which in aqueous solution, in concentrations above approximately ten percent. by weight, is a solvent for nickel ferricyanlde but which will not dissolve very appreciable amounts 'of the corresponding ferrocyanide. In other words, we employ a solution of a salt which is a selective solvent for the ferricyanide when both the ferrocyanide and ferricyanide are present. Thus, the salt employed serves as an inhibitor or retardant of reaction between the nickel salt present and the soluble ferricyanide present to form an insoluble ferricyanide precipitate. In preferred practice, such inhibitor or retardant of the precipitation, of an insoluble ferricyanide. is potas-.

sium citrate but in place thereof we may employ'any. soluble salt of a so-called -fruit acid", oxalic acid or the like, such as alkali metal tar-.

trates, oxalates, maiates, succinates, benzoates, etc. In short, the salt may be any that will provide a solution which is a selective solvent for nickel ferricy'anide when the same is present with a-corresponding ferrocyanlde. If desired, dou-' ble salts may be employed, such as potassium sodium tartrate. I

After .the first-stage treating bath has been prepared, the silver print to be toned is immersed therein untiithe. silver image is thoroughly bleached; The treated print is then re-- moved from the bath and thoroughly washed in running water until all water-soluble compounds have been removed. a

In some instanceait is desirable to remo the silver compound present on the treated prior to the second stage of treatment with a color precipitant. This may be accomplished by including hypo in the original treating bath or by treating the print with a hypo. solution after the first stage of treatment. Wherehypo is included in the treating bath the amount of such reagent present must be controlled in order that the particles of color intermediate will be deposited on the printin substantially the same distribution as theorlginal silver particles before the silver is removed in solution.

After the print from the first stage of the process has been washed, and the silver content removed if.desired, the print is 'then treated with, a color precipitant to convert the particles of color intermediate into a pigmentof red color,

after which the silver content of the print, if not previouslyremoved, is then removed in a suitable solvent. As will be apparent, the color precipitant employed will depend upon the compound deposited as a color intermediate and the final color desired in the toned print.

The following specific examples are illustrative of the practice of the present invention.

Example I According to this example the half-tone image of a silver photographic print is converted into an image. of a magenta color which is the subtractive red or minus green of subtractive color -printing. This example covers our preferred other inhibitor of reaction between a soluble nickel salt and an alkali-metal ferricyanide with the formation of a nickel ferricyanide precipitate; 30 grams of citric acid; preferably, 100 cc. formalin (40 per cent. aqueous'formaldehyde solution); and sufiicient water to make up one liter of solution. This solution may be prepared as far in advance of use as desired since it is capable of, being stored over long periods. If, howeve the solution is not to be stored over any substantial period the formaldehyde content may be reduced or omitted without entirely de-,- stroying the usefulness of the solution. However, it ispreferred to include the formaldehyde since it not only acts as a preservative for the solution but also as a hardening agent for the gelatin on the prints treated in .the solution. The formaldehyde also prevents the swelling of the gelatin emulsion on the films treated when the treating bath is used in a relatively warm surrounding atmosphere. Inasmuch as the formaldehyde does not serve its desired purpose where the treating bath is either alkaline or strongly acid, we prefer to maintain the pH value ofthe treating bath either at approximately 7 or only slightly on the acid side.

After the above solution has been prepared the first-stage treating bath is prepared by mixing 100 cc. of the above solution with 20 cc. of a 15 .per cent. solution of potassium ferricyanide' or other soluble ferricyanide of a metal which will not form an insoluble compound with any of the other ions present in the treating hath.

After the photographic print to be toned has been developed and printed in conventional manner it is thoroughly washedto remove the last trace of hypo and is then immersed in the above described treating bath for about 15 to 20 minutes, or-until the silver image on the print is thoroughly bleached. The print is then washed in running water or several changes of water to remove substantially completely all water soluble compounds present. The print is then immersed in a color precipitating bath or red developer-which is preferably prepared by mixing and heating together at about 50 C. for 30 minutes 30 grams of dimethylglyoxime, 250 cc. of

monoethanolamine, 750 cc. of triethanolamine,

' and 500 cc. of an alcohol, particularly methyl or ethyl alcohol, and thereafter adding approximately 3500 cc. of water; This color precipitah in: bath or red developer ha's the advan'rgcthat it is not precipitated by water. Whereas dimethylglyoxime itself is insoluble in water it allpe'ars that in the above solution a water soluble addition compound is formed between the dimethylglyoxime and the triethanoline. In other words, whereas a water insoluble dioxime is employed in preparing the. red developer, the dioxime product present in the finished red developer is a water-soluble compound.

An alternative red [developer consists of 10 grams of dimethylglyoxime dissolved in 200 *cc. of a mixture of 75 per cent. triethanoline and 25 per cent. monoethanolamine and sufllcient water to make up a liter of solution- This alternative color precipitating bath is prepared by heating the mixture of the two amines and the dioxime at about 100 C. for approximately minutes to effect the solution of the dioxime in the mixture of amines and to eifect what appears to be a reactionof the ingredients inasmuch as the solution which is'initially colorless turns to a pale reddish brown color. heating of the ingredients as described, there is then added the amount of water necessary to make up a liter of solution.

The print is immersed in the red developer solution for about 10 minutes, or until the red color completely develops. After the color has developed the print is removed from the bathand immersed in either a 5 per cent. solu- ,tion' of hypo or about a 10 percent. aqueous red developer containing this compound as the print a pigment consisting of nickei-dimethylglyoxime. However, any dioxime may be employed in the red developer such as alpha-benzyldioxime, methylp'ropylglyoxime, or alpha-furyl dioxime. However, the nickel compounds of these other dioximes are not true magenta in color and, therefore, where a truemagenta is desired it is preferred to employ dimethylglyoxime. While, as pointed out below inzExample -2, the solvent for the dioxime employed in preparing the red developer may consist exclusivelyof alcohol, acetone or the like, we prefer to employ a solvent comprising a mixture of amines as described above since by the use of such solvents a more brilliant color is obtained and, where the print has been prepared on strip film. the mixed amine solvent does not shrivel the collodion backing as does a solvent such as alcohol alone.

In place of the amine mixture employed as the preferred solvent in the red developer described above, we may employ as a solvent'any amine which is soluble in water and which will dissolve upward of of 1 per cent; of the dioxime employed in the red developer. For example, monoethanolamine may be used alone as a solvent for the dioxime employed. However, this compound is a little too strongly alkaline and some high light detail is lost when the print is treated in a sole solventfor the dioxime, Triethanolamine may also be used alone but the results obtainedtherewith are not completely satisfactory. It'is also possible to use tertiary amines such as tertiary butyl amine. In general, we prefer to employ aliphatic amines and to use mixtures of the same. In order to secure best results After the 'tively strong ammonia solution.

must be fairly strong alkaline and in order to obtain the desired alkalinity mixtures of the amines are employed. A red developer of optimum alkalinity is obtained when the solvent for the dioxime consists of 75 per cent. triand 25 per cent. mono-ethanolamine. Also, di-ethanolamine may be used withsuccess when mixed with 20 per cent of either monoor tri-ethanolamine.

Example 2 According to this example there is obtained a final toned print of substantially the same color as produced by the preferred practice of the process described under Example 1. However, the print is somewhat less transparent and brilliant in color although the appearance of the print is substantially superior to red toned prints prepared by any of the prior art processes of which we are aware.

According to this modification of the process,

" we first prepare a solution of the following comin the red developing, the developing bath position:

Grains Nickel nitrate i 50 Potassium citrate 300 Citric a i 20 Water 500 To each 50 cc. portion of the above solution we then add a solution of the following composition:

Grams Potassium ferricyanide 0.4 Sodium thiosulfate -2. 0.5 Water 50 After the treating bath has been prepared in the manner described above, the print to be toned is immersed in the bath until the silver image originally present on the printhas completely 'disappeared and its place has been' taken by an image formed by deposited particles of nickel ferrocyanide. This ordinarily requires approximately from 10 to 20 minutes. This image is only faintlyv visible when the print is wet and is sub-' stanti-ally invisible when the print is dry. This,

of course, is true when the print has been made upon a substantially white paper.

Inasmuch as hypo is employed in the first stage treating bath used in the present modification of the process, the silver compound formed during the treatment will be removed from the print in solution, leaving correspondingly distributed particles of nickel-ferrocyanide in place thereof.

After the print has been treated in the firststage treating bath for the required period of 'time, it is removed from the bath and thoroughly washed in running water until all water soluble compounds have been removed. Generally, the print should be washed for from 15 to 20 minutes in runnlngwater.

The washed print is then contacted with a dioxime and ammonia. Preferably, the print is immersed in a solution containing a dioxime and a water-soluble or water-miscible solvent there- I for. After the printhas been immersed in this solution for a sufficient period of time to soak up a substantial amount of the dioxime solution, it is then removed therefrom and immersed in a rela- For example, the print may be immersed in a solution of one gram of 'dimethylglyoxime dissolved in cc. of a methyl alcohol or other water-soluble or watermiscible solvent such as another alcohol, acetone or the like. :The print is allowed to remain in such'solution for about two or three minutes. or

until the image in the desired intensity of color appears,'and the print is thereafter withdrawn and immediately immersed in a reasonably strong aqueous solution of ammonia, such as a 5% ammonia solution. Such a solution may be prepared by mixing 1 part of commercial (28%) ammonia with 5 parts of water. The print is permitted to remain in the ammonia solution for about 5 to 10 minutes, after which the print is removed from the ammonia bath and washed thoroughly in running water for from approximately 10 to 20 minutes.

vW'hile in the present modification of the secondstage of the process it is desired to introduce the print first into the alcoholic solution of 'dimethyl glyoxime and thereafter into anammonia solution, it is'possi'ble to produce satisfactory results by carrying out the two operations in a single stage by adding ammonia to the alcoholic.solu-- Dimethyl glyoxime gram 1 Commercial methyl alcohol; cc 28% ammonia solution cc 10 In case the print has been made on a strip film instead of on photographic paper, approximately 40 cc. of water should be added to the above solution to prevent the curling of the film of Celluloid in the strip film.

As pointed out in the above examples. we preferably remove the silver content of a photographic print during .the toning operation or after the production of the toned print with an alkali-metal thiosulfate, such as a conventional hypo solution. We have discovered that such use of an alkali-metal thiosulfate can advantageously be eliminated in the toning procedure by substivtuting therefor a small amount of potassium thiocyanate or other alkali-metal thiocyanate, including ammonium thiocyanate.

The greatest commercial importance of the present invention resides in its applicability to the toning of the red color component image in the preparation of natural-color photographic prints prepared from color separation negatives. As is well known, color separation negatives are I made by photographing the subject on three separate prints or films through three standard color filters, namely, red, green and blue filters. Each of these negatives constitutes a separate record -of each of these primary colors. Positives are prepared from the color separation negatives and these positives are toned in the primary colors. The positive prints made from the red filter negative being toned. blue-green, the print from the green filter negative being toned magenta, and

the print from the blue filter negative being from color separation. negatives is-not new in the art. However, the prior art processes of making natural-color photographs from color separation negatives have left much to be desiredin the way of photographic excellence. The

method described below "for the toning of the red color component image constitutes a material improvement in the art of making natural-color photographs. l

After the positive prints have been. prepared on strip filni or the like from color separation negatives in accordance with the conventional practice, the positive to be toned magenta is transferred to a tray containing a treating bath prepared by mixing 20 cc. of fifteen per cent. solution of potassium ferricyanide with 100 cc. of a solution of the following composition:

Nickel chloride "grams" 50 Potassium citrate do 300 Citrlc'acid do 30 Formalin cc 100 Sumcient water to make up one liter.

The tray containing the above treating bath is rockedto expel air-bubbles from under the film and'to insure rapid and uniform immersion of the film. The tray is then set aside until the first stage of treatment has been completed, which takes from fifteen to twenty minutes.

When the print has been thoroughly bleached,

it is'removed from the first-stage treating bath and placed in another tray containing fresh water and the film washed by changing the water in the tray about four times, each time making certain that the film floats free of the bottom of the tray so as not to entrap chemicals beneath it. After washing, thelprint is introduced into another tray and there is added sufi'icient amount of a red developer to cover the'film, the tray then being set aside. The red developer preferably is prepared by mixing and heating together at about 50 C., for about thirty minutes, 30' grams of dimethylglyoxime, 750 cc. of triethanolamine, 250 cc. of monoethanolainine, and 500 of methyl or ethyl alcohol. Thereafter, there is added about 3500 cc. of water to make up the final developing solution. After about ten minutes, the red developer is poured off the film immersed therein and the film is then treated with a 25 per cent. solution of hypo for about five minutes. Thereafter, the film is washed with three or four changes of water, following which the film is immersed for a few seconds in a 1 per cent. solution of acetic acid and washed again with two or three changes of water. Thereafter, the resulting magenta print is ready for mounting.

While we have described in. detail preferred embodiments of our invention, it will be understood that the details of procedure may be variously modified without departing from the spirit of the invention or the scope of the subjoined claims.

We claim:

1. In a process of toning a silver photographic print in which the silver image is replaced at least in part with a nickel-dioxime image, the improvement which comprises immersing the print in an aqueous treating bath whose constituent ingredients include a soluble nickel salt,

a soluble ferrlcyanide, a soluble salt of an hydroxy aliphatic acid capable of forming a complex metal-acid ion, and thereafter immersing the print in a solution of a dioxime compound dissolved in a solvent comprisinga water-soluble amine. i

2. In a process of toning a silver photographic print in which the silver image is replaced at least in part with a nickel-dioxime image, the improvement which comprises immersing the print in an aqueous treating bath whose constituent ingredients include a soluble nickel salt, a

soluble ferricyanide, a soluble salt of an hydroxy aliphatic acid capable of forming a complex metal-acid ion, and thereafter immersing the print in a solution of a 'dioxime compound dissolved in a solvent comprising a. mixture of water-soluble aliphatic amines.

3. In a process of toning a silver photographic print in which the silver image is replaced at least in part with a nickel-dioxime image, the improvement which comprises immersing the .print in'an aqueous treating bath whose constituent ingredients include a soluble nickel salt, a soluble ferricyanide, a soluble salt of an hydroxy aliphatic acid capable of forming a complex metal-acid ion, and thereafter immersing the print in a solution of a dioxime compound dissolved in a solvent comprising monoethanolamine and triethanolamine.

4. In a process of toning a silver photographic print in which the silver image is replaced at least in part with a nickel-dioxime image, the improvement which comprises immersing the print in an aqueous treating bath whose constituent ingredients include a soluble nickel salt, a soluble ferricyanide, and asoluble salt of an organic acid which in solution will prevent the precipitation of nickel ferricyanide while allowing precipitation. of nickel ferrocyanide, selected from the group consisting of tartrates, citrates,

oxalates, malates, succinates and benzoates, and.

thereafter immersing the print in a solution of a dioxime compound dissolved in a solvent comprising a water-soluble amine capable of dissolving upward of one-tenth of 1 per cent. of the dioxime. Y

5. In a process of toning a silver photographic print in which the silver image is replaoed'at least in part with a nickel-dioxime image, the

improvement which comprises immersing theprint in an aqueous treating bath whose constituent ingredients include a soluble nicket salt, a soluble ferricyanide, and a soluble salt of an organic acid which in solution will prevent the precipitation of nickel ferricyanide while allowing precipitation of nickel -ferrocyanide,. selected from the group consisting of tartrates, citrates, ,ox-alates, malates, succinates and benzoates, and

- consisting of tartrates,citrates, oxalates, malates,

aqueous treating bath whose constituent ingre-Q succinates and benzoates, and thereafter immersing the print in a solution of a color-developer comprising dimethylglyoxime dissolved in a solvent comprising a water-soluble amine capable of dissolving upward of one-tenth of 1 per cent.

of the dimethylglyoxime.

'7. In a. process of toning a silver photographic print in which the silver image is replaced at least in part with a nickel-dioxime image, t he improve,- ment which comprises immersing the print in an dients include a soluble nickel salt, a soluble ferricyanide, and a soluble saltof an organic acid which in solution will prevent the-precipitation of nickelferricyanide while allowing precipitation ofnickel ferrocyanide, selected from the group consisting of tartrates, citrates, oxalates, malates, succinates and benzoates, and thereafter print.

immersing the print in a solution 'ofa colordeveloper comprising dimethylglyoxime dissolved in a solvent comprising a mixture of water-soluble aliphatic amines.

8. In a process of toning a silver photographic print in' which the silver image is replaced at least in part with a nickel-dioximeimage, the improvement which comprises immersing the print in an acidified aqueous treating bath whose constituent ingredients include a soluble nickel salt, a soluble ferricyanide, and a soluble salt of an hydroxy aliphatic acid capable of forming a complex metal-acid ion, removing from the print the silver compound formed by dissolving the same in a solution of a solvent reagentselected from the group consisting of soluble thiosulfates and thiocyanates, and thereafter immersing the print in a solution of a dioxime compound.

9. In a process of toning a silver photographic print in which the silver image is replaced at least in partwith a. nickel-dioxime image, the

improvement which comprises immersing the print in an acidified aqueous treating bath whose constituent ingredients include a soluble nickel salt, a soluble ferricyanide, and a soluble salt of i an hydroxy aliphatic acid capable of forming a complex metal-acid ion,'thereafter immersing the print in .a solution of a dioxime compound, and

thereafter removing from the print the silver compound formed by dissolving the same'in a solution of a solvent reagent selectedlfrom the group consisting of soluble thiosulfates and thiocyanates. v

10. In a process of toning a silver photographic print in which the silver image is replaced'at least in part with a nickel-dioxime image, the improvement which comprises immersing the print in an acidified aqueous treating bath whose constituent ingredients include a. soluble nickel salt, a soluble ferricyanide, a soluble salt of an organic acid which in solution will prevent the precipitation of nickel ferricyanide while allowing precipitation of nickel ferrocyanide, selected from the group consisting of tartrates, citrates,

oxalates, m-alates, succinates and benzoates, and" formaldehyde, washing the resulting print, im-

mersing the washed print in a-solution of a colordeveloper comprising dimethylglyoxime in' a solvent comprising monoethanolamine and triethanolarnine, washing the resulting print, removing the silver salt present on the print by dissolving the same in a solvent selected from the. group consisting of water-soluble thiosulfates and 'thiocyanates, and washing the resulting 11'. In a process of toning a silver photographic print in which the silver image is replaced at least in part with a nickel-dioxime image, the improvement which comprises immersing the print in an acidified aqueous treating bath whose constituent ingredients include a soluble nickel salt, a soluble ferricyanide, a soluble salt of an organic acid which in solution will. prevent the precipitation of nickel ferricyanide while allowing precipitation of nickel ferrocyanide, and a solvent for silver salts, washing the resulting print, immersing the washed print in a solution of a color-developer comprising dimethylgly oxime, and washing the resulting print.

' 12. Ina process of toning a silver photographic print in which the silver image is replaced at to f least in, part with a nickel-dioxime image, the

improvement which comprises immersing the print in an acidified aqueous treating bathwhose constituent ingredients include a. soluble nickel salt, a soluble ferrlcyanlde, a. soluble salt of an organic acid which in solution will prevent the precipitation of nickel ferricyamde while allowing precipitation of nickel ferrocyanide, and a solvent for silver salts comprising potassium thiocyanate,

washing the resulting print, immersing the washed print in a. solution of a. dloxlme compound -and washing the resulting print.

\ FRANCIS H. SNYDER. HENRY W. RIMIBACH. 

